Process for hydrotreating a hydrocarbon oil

ABSTRACT

A process or hydrotreating a hydrocarbon oil that employs a first reactor and a second reactor. The hydrocarbon oil is hydrotreated in the first reactor with a first hydrotreating catalyst in the presence of a first stream of hydrogen-containing gas to obtain a first effluent. The first effluent is separated using a stripping column to provide a hydrotreated hydrocarbon oil and used hydrogen-containing gas. A second stream of hydrogen-containing gas is heated within a section of a heating device arranged upstream of the first reactor to obtain a stream of heated hydrogen-containing gas. The stream of heated hydrogen-containing gas is contacted in the second reactor in the presence of at least part of the hydrotreated hydrocarbon oil with a second hydrotreating catalyst to obtain a second effluent which comprises a further hydrotreated hydrocarbon oil.

FIELD OF THE INVENTION

The present invention relates to a process for hydrotreating a hydrocarbon oil employing at least a first and a second reactor.

BACKGROUND OF THE INVENTION

Processes for hydrotreating hydrocarbon oils are well known. Also processes that employ two or more reactors have been described in the literature.

Processes for reducing the amount of sulphur or nitrogen containing compounds and aromatics, are in general called hydrotreating processes. These processes can be further divided into processes which are especially directed at saturation of unsaturated compounds such as aromatics and olefins, in which case they are called hydrogenation processes, and processes which are especially directed at reducing the amount of sulphur containing compounds and often at the same time also of nitrogen containing compounds, in which case they are called hydrodesulphurisation processes. There are also processes which are specifically directed at reducing the amount of nitrogen containing compounds and in which only a relatively small amount of sulphur-containing compounds are removed. These are called hydrodenitrogenation processes. With the expression hydrodesulphurisation processes, which is used hereinafter, processes are meant which are directed at removal of sulphur-containing compounds and optionally an amount of nitrogen. Processes wherein linear waxy hydrocarbons are isomerised to branched alkanes are referred to as hydroisomerisation or as hydrodewaxing processes. These processes can be applied to middle distillates so that the pour point is reduced. Alternatively, the process can be applied to lubricating oils to enhance the viscosity index.

A hydrotreating process using two reactors in series has been described in WO 2011/006952 A2. It describes a hydrotreating process in which process a combination of a hydrocarbon oil and a hydrogen-containing gas is passed through a first furnace and the heated combination is contacted with a hydrotreating catalyst in first reactor vessel. The effluent of this contact is separated into partly hydrotreated hydrocarbon oil and contaminated hydrogen-containing gas. The separation is carried out in a stripping column using hydrogen as stripping gas. The partly hydrotreated hydrocarbon oil is passed through a second furnace and the heated oil is contacted in a second reactor vessel with a hydrotreating catalyst in the presence of a hydrogen-containing gas. The product of this step is separated into a hydrotreated hydrocarbon oil and used hydrogen-containing gas, which hydrotreated hydrocarbon oil can be recovered as product, and which used hydrogen-containing gas is recycled to the stripping column.

Since product properties demand change during the year in the sense that cold flow properties of the product are less stringent during summer than the other months of the year, it is desirable to have a flexible hydrotreating process in which the first and second hydrotreating steps can attractively be decoupled. Such decoupling would allow the use of the first reactor vessel only during summer and the integration of the two reactor vessels during the remaining part of the year. A major difficulty is, however, the start-up of the second hydrotreating step once the two hydrotreating steps need to be integrated again because the second reactor vessel can easily be damaged during the start-up process. Object of the present invention is to provide a process which facilitates the coupling of the two reactor vessels in an attractive manner, whilst enhancing the economics of the integrated process.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a process for hydrotreating a hydrocarbon oil employing at least a first reactor and a second reactor, which process comprises:

(i) providing a first stream of hydrogen-containing gas; (ii) hydrotreating the hydrocarbon oil in the first reactor with a first hydrotreating catalyst in the presence of the first stream of hydrogen-containing gas as provided in step (i) to obtain a first effluent; (iii) separating the first effluent as obtained in step (ii) into a hydrotreated hydrocarbon oil and used hydrogen-containing gas using a stripping column employing a hydrogen-containing gas as stripping gas; (iv) providing a second stream of hydrogen-containing gas which is heated within a section of a heating device which is arranged upstream of the first reactor to obtain a stream of heated hydrogen-containing gas; and (v) contacting in the second reactor at least part of the stream of heated hydrogen-containing gas as obtained in step (iv), optionally in the presence of at least part of the hydrotreated hydrocarbon oil as obtained in step (iii), with a second hydrotreating catalyst to obtain a stream of used hydrogen-containing gas, and a second effluent which comprises a further hydrotreated hydrocarbon oil when hydrotreated hydrocarbon oil as obtained in step (iii) is also present.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the present invention the second stream of clean hydrogen-containing gas is heated within a section of a heating device which is arranged upstream of the first reactor to obtain a stream of heated clean hydrogen-containing gas.

Suitably, the first stream of hydrogen-containing and/or the hydrocarbon oil are heated within the same heating device before the heated combination is passed to the first reactor. In a particular embodiment of the present invention the first stream of hydrogen-containing and the hydrocarbon oil are combined and heated within a lower section of the heating device before the heated combination is passed to the first reactor, whereas the second stream of hydrogen-containing gas is heated in an upper section of the heating device. In this way, the economics of the integrated process are considerably improved since a separate second furnace upstream the second reactor vessel is no longer required, whereas at the same time the use of such a heating device allows the warming-up of the second hydrogen-containing gas in a highly controlled and flexible manner once the operation of the second reactor needs to be integrated again with operation of the first reactor after it has been decoupled during the summer.

The present invention includes the warming-up phase of the second reactor. During said phase the second stream of heated hydrogen-containing gas is passed to the second reactor which allows the second reactor to warm-up and to become pressurized in a controlled manner. Once the second reactor has been heated to the desired temperature it can be pressurized. An additional advantage of the present process is that during the warming-up of the second reactor the hydrotreating catalyst inside the second reactor can suitably be reduced by means of the second stream of heated hydrogen-containing gas before the second reactor is integrated again in operation with the first reactor. Suitably, such a warming-up process the temperature in the reactor is gradually increased. The increase in temperature can suitably be in the range of from 5-40° C./hour. Once a temperature is reached in the range of from 240-350° C., the second hydrotreating catalyst can suitably be reduced for a period of time of 4-16 hours, preferably 6-10 hours, before the operation of the second reactor is integrated again with the operation of the first reactor. Another advantage of the present process is that the second stream of heated hydrogen-containing gas can suitably be used to strip off hydrocarbon oil which is present on the second hydrotreating catalyst before the second reactor is decoupled or at least part of the second hydrotreating catalyst is replaced.

In accordance with the present invention the first stream of clean hydrogen-containing gas and the second stream of hydrogen-containing gas are preferably derived from the same source of clean hydrogen-containing gas. During the period that the second reactor cannot be pressurised, the spare compressor might be used to circulate the stream of hydrogen-containing gas.

In general it will be advantageous to hydrotreat a hydrocarbon oil of which a major amount, for example more than 70% by weight, suitably more than 80% by weight and preferably more than 90% by weight, is in the liquid phase at the process conditions prevailing in the first reactor. Hydrocarbon oils that can suitably be hydrotreated according to the present invention are kerosene fractions, gas oil fractions and lubricating oils. Especially a gas oil fraction can very suitably be subjected to the present invention, as the environmental constraints on gas oils are tightening. A suitable gas oil would be one of which a major portion of the hydrocarbons, e.g. at least 75% by weight boils in the range of from 150 to 400° C. A suitable lubricating oil contains at least 95% by weight of hydrocarbons boiling in the range of from 320 to 600° C.

The hydrotreating process can be a hydrofinishing process in which the hydrocarbon oil is marginally changed, it may be a hydrocracking process in which the average number of carbon atoms in the oil molecules is reduced, it may be a hydrodemetallisation process in which metal components are removed from the hydrocarbon oil, it may be a hydrogenation process in which unsaturated hydrocarbons are hydrogenated and saturated, it may be a hydrodewaxing process in which straight chain molecules are isomerised, or it may be a hydrodesulphurisation process in which sulphur compounds are removed from the feedstock. It has been found that the present process is particularly useful when the hydrocarbon oil comprises sulphur compounds and the hydrotreating conditions comprise hydrodesulphurisation conditions. The process is also very advantageous in the treatment of sulphur-containing hydrocarbon oils that contain so-called refractory sulphur compounds, i.e., dibenzothiophene compounds.

The hydrotreating conditions that can be applied in the process of the present invention are not critical and can be adjusted to the type of conversion to which the hydrocarbon oil is being subjected. Generally, the hydrotreating conditions in steps (ii) and (v) comprise a temperature ranging from 250 to 480° C., preferably from 320 to 400° C., a pressure from 10 to 150 bar, preferably 20 to 90 bar, and a weight hourly space velocity of from 0.1 to 10 hr⁻¹, preferably from 0.4 to 4 hr⁻¹. The skilled person will be able to adapt the conditions in accordance with the type of feedstock and the desired hydrotreatment.

Preferably, the second stream of hydrogen-containing gas as provided in step (iv) contains less than 0.1% by volume of hydrogen sulphide.

The hydrotreating catalyst in step (ii) is suitably a hydrodesulphurization catalyst and the hydrotreating catalyst in step (v) is suitably a hydrodewaxing catalyst

Suitably, the hydrodesulphurization catalyst as used in step (ii) comprises one or more metals from Group VB, VIB and VIII of the Periodic Table of the Elements, on a solid carrier.

Suitably, the hydrodewaxing catalyst as used in step (v) comprises as catalytically active metal one or more noble metals from Group VIII of the Periodic Table of the Elements on a solid carrier.

Suitable catalysts comprise at least one Group VB, VIB and/or VIII metal of the Periodic Table of the Elements on a suitable carrier. Examples of suitable metals include cobalt, nickel, molybdenum and tungsten, but also noble metals may be used such as palladium or platinum. Especially when the hydrocarbon oil comprises sulphur, the catalyst suitably contains a carrier and at least one Group VIB and a Group VIII metal. Whereas these metals can be present in the form of their oxides, it is preferred to use the metals in the form of their sulphides. Since the catalyst may normally be produced in their oxidic form the catalysts may subsequently be subjected to a pre-sulphiding treatment which can be carried out ex situ, but is conducted preferably in-situ, in particular under circumstances that resemble the actual conversion.

The metals are suitably combined on a carrier. The carrier may be an amorphous refractory oxide, such as silica, alumina or silica alumina. Also other oxides, such as zirconia, titania or germania can be used. For hydrodewaxing processes, crystalline aluminosilicates, such as zeolite beta, ZSM-5, mordenite, ferrierite, ZSM-11, ZSM-12, ZSM-23 and other medium pore zeolites, can be used. When the hydrotreating conditions entail hydrocracking, the catalyst may advantageously comprise a different zeolite. Suitable zeolites are of the faujasite type, such as zeolite X or Y, in particular ultra-stable zeolite Y. Other, preferably large pore, zeolites are also possible. The zeolites are generally combined with an amorphous binder, such as alumina. The metals are suitably combined with the catalyst by impregnation, soaking, co-mulling, kneading or, additionally in the case of zeolites, by ion exchange. It is evident that the skilled person will know what catalysts are suitable and how such catalysts can be prepared.

The first and second hydrotreating catalysts can be present in the respective reactor in one or more beds.

Suitably, at least part of the stream of used hydrogen-containing gas as obtained in step (v) can be used as stripping gas in step (iii).

Also gaseous hydrocarbons that may have been formed in the second hydrotreating reactor may be used in the stripping action. Moreover, since the stream of used hydrogen-containing gas as obtained in step (v) emerges from the second hydrotreating reactor, it may become available at hydrotreating conditions, which entails elevated temperature. The stream of used hydrogen-containing gas at such elevated temperature will facilitate the stripping action further and will improve the heat recovery from the used hydrogen-containing gas.

Suitably, both the first and second stream of hydrocarbon-containing gas comprise a clean hydrogen-containing gas. By “clean hydrogen-containing gas” is understood a gas that contains less than 0.1% vol of hydrogen sulphide, based on the total volume of the gas, preferably less than 0.01% vol, more preferably less than 20 ppmv, and most preferably less than 5 ppmv. Examples of clean hydrogen-containing gas may include fresh make-up hydrogen, prepared by e.g., steam reforming, or a contaminated hydrogen-containing gas that has been subjected to a cleaning treatment, e.g., with an amine. Such contaminated gas may originate from the present process, but also contaminated hydrogen-containing gas from different sources or processes may be subjected to cleaning and subsequent use in the present process. The amount of hydrogen in clean hydrogen-containing gas is preferably at least 95% vol, more preferably at least 97% vol, based on the total clean hydrogen-containing gas.

In a first embodiment the hydrogen-containing gas that is used in step (ii) in the first reactor is clean hydrogen-containing gas. This ensures that the amount of gas that needs to be fed into the first reactor can be minimised. Such gas may suitably be obtained from purification of contaminated hydrogen-containing gas, e.g., such contaminated gas that becomes available in the present process.

In a preferred embodiment the effluent from the first reactor is passed to a gas-liquid separator before using the stripping column. The gaseous phase in the effluent typically contains large amounts, such as 0.5 to 5.0% vol, based on the total volume of the gaseous phase, of contaminants such as hydrogen sulphide. This phase is therefore withdrawn as contaminated hydrogen-containing gas in the gas-liquid separator and may preferably be passed to a purification section, such as an amine scrubber. The liquid phase comprising partly hydrotreated hydrocarbon oil is withdrawn from the gas-liquid separator and passed to the stripping column. The stripping column is operated with at least part of the stream of used hydrogen-containing gas as obtained in step (v) from the second reactor. The combination of the stream of used hydrogen-containing gas and stripped gas as obtained in step (iii) can be fed to the first reactor as hydrogen-containing gas. It is clear that in such an embodiment the first effluent is passed to a gas-liquid separator before using the stripping column. The majority of the contaminants will have been removed in the gas liquid separator.

It will be understood that in the hydrotreatment processes in steps (ii) and (v) hydrogen will be consumed. Generally, the hydrogen consumption for the hydrotreatment steps is not critical for the process and depends on the type of hydrocarbon oil that is being processed. Suitably, the hydrogen consumption in each of the reactors under hydrotreatment conditions ranges from 0.1 to 2.5% wt, based on the weight of the hydrocarbon oil for the first reactor and on the weight of the partly hydrotreated hydrocarbon oil for the second reactor. The hydrogen consumed in the first and second reactor is suitably being supplemented for at least 80% by addition of clean hydrogen-containing gas to the second reactor. In this way the amount of gas that gets contaminated with significant amounts of contaminants in the first reactor is minimised. Further minimisation can suitably be achieved by supplementing at least 90%, more preferably substantially 100% of the hydrogen consumed in the first and second reactor, with clean hydrogen-containing gas to the second reactor.

The first effluent from the first reactor contains partly hydrotreated hydrocarbon oil. In step (iii) this partly hydrotreated hydrocarbon oil is separated from contaminated hydrogen-containing gas. In an advantageous embodiment the hydrocarbon oil to be treated is a gas oil that typically contains sulphur compounds. In the first reactor these sulphur compounds are converted to hydrogen sulphide, which contaminates the hydrogen-containing gas. In accordance with the process of the present invention the contaminated hydrogen-containing gas is separated in step (iii) from the partly hydrotreated hydrocarbon oil in a stripping column. In the stripping process a hydrogen-containing gas, preferably at least part of the stream of used hydrogen-containing gas as recovered from step (v), is being used as stripping gas. The contaminated hydrogen-containing gas thus obtained in the stripping column is suitably cleaned and used again as clean hydrogen-containing gas in step (v), and optionally in step (ii).

The treatment of contaminated hydrogen-containing gases, especially when contaminated with hydrogen sulphide and other sulphur compounds, such as carbon disulphide or carbon oxysulphide, is well known. A suitable way to remove these contaminants has been briefly described in EP-A 611 816, and is by amine scrubbing. Therefore, the contaminated hydrogen-containing gas is preferably cleaned by treating with an amine.

In such situations the contaminated hydrogen-containing gas is suitably contacted with an aqueous amine solution. The aqueous solution comprises one or more amine compounds Suitable amine compounds are primary, secondary and tertiary amines. Preferably, the amines comprise at least one hydroxyalkyl moiety. The alkyl group in such moiety suitably comprises from 1 to 4 carbon atoms. In case of secondary and tertiary amines, the amine compounds preferably comprise one or more alkyl and hydroxyalkyl groups each with preferably from 1 to 4 carbon atoms. Suitable examples of amine compounds include monoethanol amine, monomethanol amine, monomethyl-ethanolamine, diethyl-monoethanolamine, diethanolamine, triethanolamine, di-isopropanolamine, diethyleneglycol monoamine, methyldiethanolamine and mixtures thereof. Other suitable compounds are N,N′-di(hydroxyalkyl) piperazine, N,N,N′,N′-tetrakis(hydroxyalkyl)-1,6-hexanediamine, in which the alkyl moiety may comprise from 1 to 4 carbon atoms.

The aqueous solution may also comprise physical solvents. Suitable physical solvents include tetramethylene sulphone (sulpholane) and derivatives, amides of aliphatic carboxylic acids, N-alkyl pyrrolidone, in particular N-methyl pyrrolidine, N-alkyl piperidones, in particular N-methyl piperidone, methanol, ethanol, ethylene glycol, polyethylene glycols, mono- or di(C₁-C₄)alkyl ethers of ethylene glycol or polyethylene glycols, suitably having a molecular weight from 50 to 800, and mixtures thereof.

The concentration of the amine compound in the aqueous solution may vary within wide ranges. The skilled person will be able to determine suitable concentrations without undue burden. Advantageously, the aqueous solution comprises at least 15% wt of water, from 10 to 65% wt, preferably from 30 to 55% wt of amine compounds and from 0 to 40% wt of physical solvent, all percentages based on the weight of water, amine compound and physical solvent.

The conditions under which the contaminated hydrogen-containing gas is being treated with an amine suitably include a temperature of from 0 to 150° C., preferably, from 10 to 60° C., and a pressure of from 10 to 150 bar, preferably from 35 to 120 bar.

The stripping gas in the stripping column comprises a hydrogen-containing gas. Since at least part of the stripping gas can suitably become available from the hydrotreatment reaction in step (v), it becomes available at elevated temperature. Since the elevated temperature has an improved stripping performance over the stripping performance of cool gas and counteracts the cooling effect of stripping, it is evidently clear that the present process provides an additional advantage in that an improved stripping action is being obtained. The hydrogen-containing gas that is being used as stripping gas in step (iii) has advantageously a temperature of from 250 to 480° C., preferably from 320 to 400° C.

A portion of or the entire partly hydrotreated hydrocarbon oil is subjected to a further hydrotreatment in step (v). As indicated above, the present process is especially advantageous when the hydrocarbon oil to be treated is a gas oil. Therefore, it is particularly preferred that the hydrotreating catalyst in step (ii) is a hydrodesulphurisation catalyst and the hydrotreating catalyst in step (v) is a hydrodewaxing catalyst. In such cases the hydrodesulphurization catalyst suitably comprises an optionally sulphided catalyst comprising one or more metals from Group V, VI and VIII of the Periodic Table of the Elements, on a solid carrier. As indicated earlier the solid carrier can be selected from any of the refractory oxides described above. The hydrodesulphurisation catalyst in particular may comprise one or more of the metals nickel and cobalt, and one or more of the metals molybdenum and tungsten. The catalyst may advantageously be sulphided as described above.

The hydrodewaxing catalyst suitably comprises as catalytically active metal one or more noble metals from Group VIIII of the Periodic Table of the Elements on a solid carrier. Preferably the noble metal is selected from the group consisting of platinum, palladium, iridium and ruthenium. The carrier advantageously comprises a zeolite as described above in combination with a binder material. Suitable binder material includes alumina, silica and silica-alumina. However, other refractory oxides can also be used.

As indicated before, the present process can suitably be used during the start-up period of the second reactor or just before the second reactor is decoupled from the first reactor.

Accordingly, the present invention also provides in one embodiment a process for hydrotreating a hydrocarbon oil employing at least a first reactor and a second reactor, which process comprises:

(i) providing a first stream of hydrogen-containing gas; (ii) hydrotreating the hydrocarbon oil in the first reactor with a first hydrotreating catalyst in the presence of the first stream of hydrogen-containing gas as provided in step (i) to obtain a first effluent; (iii) separating the first effluent as obtained in step (ii) into a hydrotreated hydrocarbon oil and used hydrogen-containing gas using a stripping column employing a hydrogen-containing gas as stripping gas; (iv) providing a second stream of hydrogen-containing gas which is heated within a section of a heating device which is arranged upstream of the first reactor to obtain a stream of heated hydrogen-containing gas; and (v) contacting in the second reactor at least part of the stream of heated hydrogen-containing gas as obtained in step (iv) with a second hydrotreating catalyst to obtain a stream of used hydrogen-containing gas.

It will be appreciated that in such embodiments of (a) starting-up the second reactor or (b) stripping hydrocarbon oil from the second hydrotreating catalyst prior to decoupling the second reactor no partly hydrotreated hydrocarbon oil will be passed to the second reactor.

The present invention also provides a hydrotreating process wherein the operation of the first and second reactors is integrated.

Hence, the present invention also provides in a second embodiment a process for hydrotreating a hydrocarbon oil employing at least a first reactor and a second reactor, which process comprises:

(i) providing a first stream of hydrogen-containing gas; (ii) hydrotreating the hydrocarbon oil in the first reactor with a first hydrotreating catalyst in the presence of the first stream of hydrogen-containing gas as provided in step (i) to obtain a first effluent; (iii) separating the first effluent as obtained in step (ii) into a hydrotreated hydrocarbon oil and used hydrogen-containing gas using a stripping column employing a hydrogen-containing gas as stripping gas; (iv) providing a second stream of hydrogen-containing gas which is heated within a section of a heating device which is arranged upstream of the first reactor to obtain a stream of heated hydrogen-containing gas; and (v) contacting in the second reactor at least part of the stream of heated hydrogen-containing gas as obtained in step (iv) in the presence of at least part of the hydrotreated hydrocarbon oil as obtained in step (iii), with a second hydrotreating catalyst to obtain a stream of used hydrogen-containing gas, and a second effluent which comprises a further hydrotreated hydrocarbon oil.

In a step (vi) the second effluent of the hydrotreatment in the second reactor can be recovered and separated into a hydrotreated hydrocarbon oil and stream of used hydrogen-containing gas. In accordance with the present invention in a step (vii) at least part of the stream of used hydrogen-containing gas can be transferred to step (iii) for use as stripping gas. Preferably, at least 90% vol of the stream of used hydrogen-containing gas is transferred to step (iii), more preferably at least 95% vol, and most preferably, the entire volume of the stream of used hydrogen-containing gas is transferred to step (iii).

The separation in step (vi) can be carried out in any suitable way. A suitable method involves the use of separation means inside the second reactor comprising a downwardly extending plate having an opening between the lower edge of the plate and the wall of the reactor. Preferably, a downwardly extending flange has been provided at the lower edge of the plate. This is in accordance with a similar plate that has been described in EP-A 611 861. Alternatively, different separation trays can be used in the lower part of the second reactor. In a further embodiment, the separation of the effluent of the hydrotreatment in the second reactor is performed in a separate gas-liquid separator, optionally with additional heat integration. The effluent, before or after separation, can suitably be used for heat exchange with the partly hydrotreated hydrocarbon oil emerging from the stripping column. This has the advantage that the effluent is cooled whilst the partly hydrotreated hydrocarbon oil can be heated to the desired hydrotreating temperature without the use of an additional furnace. It will be evident that such represents a considerable economical and heat-efficient advantage.

FIG. 1 shows a simplified flow scheme of the two embodiments of the present invention.

FIG. 2 shows a simplified flow scheme of a further embodiment of the present invention.

FIG. 1 shows a line 1 via which a hydrocarbon oil is passed trough a heat exchanger 2 and to which clean hydrogen-containing gas is added via a line 3 e, either upstream or downstream of heat exchanger 2. The combination of hydrogen-containing gas and hydrocarbon oil is passed through a lower section of a furnace 4 and the heated combination is passed via a line 5 to a first hydrotreating reactor 6. The first hydrotreating reactor 6 has been provided with three catalyst. Between subsequent beds a quench, for instance clean hydrogen-containing gas, is added via lines 3 c and 3 d, respectively. In principle, the flow in the first and second reactor can be upwards or downwards. It is preferred to pass the hydrogen-containing gases and hydrocarbon oil or partly hydrotreated hydrocarbon oil cocurrently through the reactor vessels in a downflow direction. In this way the gas flow and the liquid flow can be controlled in a reliable way. Further, reaction temperatures may be more easily controlled. The effluent from the first reactor is withdrawn via a line 7. The effluent is also passed through heat exchanger 2 to preheat the hydrocarbon oil to be treated, and subsequently passed to a stripping column 8. In the stripping column stripping gas in the form of used hydrogen-containing gas is fed into the lower part via a line 10 and the gaseous components in the effluent from line 7 together with the stripping gas are withdrawn as contaminated hydrogen-containing gas via a line 9. The contaminated hydrogen-containing gas is treated in an amine absorption column 16 and purified, clean hydrogen-containing gas is recovered via a line 3. The line 3 is split into the line 3 a that leads hydrogen-containing gas to the hydrocarbon oil, a line 3 b that splits subsequently into lines 3 c and 3 d to provide the first reactor 6 with additional hydrogen for reactor temperature control, and the line 3 e via which hydrogen-containing gas is heated in an upper section of the furnace 4. The heated hydrogen-containing gas so obtained is then via line 14 combined with the partly hydrotreated hydrocarbon in line 11 and the combined streams so obtained are then introduced into a second reactor 12 via line 23. It is appreciated that whereas the amine absorption is shown in the Figure as a single absorption column 16 the amine treatment unit comprises absorption and desorption columns and, optionally, one or more compressors. Further, the clean hydrogen-containing gas in the line 3 may be subjected to heat exchange with one or more other process streams, such as the contaminated hydrogen-containing gas in the line 9 and/or the effluent from the first reactor in the line 7. Stripped, partly hydrotreated hydrocarbon oil is discharged from the stripping column 8 via a line 11, whereby during integrated operation of the two reactors valve 17 is closed. The partly hydrotreated hydrocarbon oil in the line 11 can be passed to the second reactor 12. In accordance with the present invention at least 80% of the hydrogen consumed in reactors 6 and 12 will be added to reactor 12. It will be evident to the skilled person, that, if desired, a portion of fresh make-up hydrogen, i.e. up to 20% of the hydrogen gas stream, can be supplemented with a stream of hydrogen-containing gas from line 3. The treated hydrocarbon oil from reactor 12 is separated into a gaseous and a liquid stream, either inside the reactor with the aid of a special separation tray 13 or in a separate knock-out drum. The gaseous components, i.e. used hydrogen-containing gas, is withdrawn from the reactor 12 via the line 10, which passes the used hydrogen-containing gas to the stripping column 8. Liquid hydrotreated hydrocarbon oil is recovered via a line 15. The products in line 15 may be fractionated in any known manner. During the start-up process of reactor 2, just prior to the decoupling of reactor 12 when hydrocarbon oil is stripped from the catalyst in reactor 12, or when catalyst is to be replace in reactor 12, clean heated hydrogen-containing gas is allowed to enter the reactor 12 via line 14, whereas the flow of partly hydrotreated hydrocarbon oil is no longer allowed to pass to the reactor 12 by way of a closed valve 20, and partly hydrotreated hydrocarbon oil can be recovered via line 21 via open valve 17. When the reactor 12 is completely decoupled from reactor 6, also the flow of hydrogen to the reactor 12 via line 14 will be discontinued by means of closed valves 19 and 22, and the withdrawal of effluent from reactor 12 will be stopped by way of closed valve 18. Further, at least part of the hydrogen-containing gas may surpass the furnace 4 via line 21 and valve 22 and can be combined with the heated hydrogen-containing gas in line 14.

In a further embodiment of the invention, shown in FIG. 2, a line 24 is added to circulate the stream of hydrogen-containing gas. Valves 25 and 26 have been added. The line 3 is now split into the line 3 e that leads hydrogen-containing gas to the hydrocarbon oil, a line 3 b that splits subsequently into lines 3 c and 3 d to provide the first reactor 6 with additional hydrogen for reactor temperature control, and the line 3 a via which hydrogen-containing gas is heated in an upper section of the furnace 4. During the period that the second reactor cannot be pressurised, the spare compressor can be used to circulate the stream of hydrogen-containing gas via line 24 and closing valves 25 and 26. 

1. A process for hydrotreating a hydrocarbon oil employing at least a first reactor and a second reactor, which process comprises: (i) providing a first stream of hydrogen-containing gas; (ii) hydrotreating the hydrocarbon oil in the first reactor with a first hydrotreating catalyst in the presence of the first stream of hydrogen-containing gas as provided in step (i) to obtain a first effluent; (iii) separating the first effluent as obtained in step (ii) into a hydrotreated hydrocarbon oil and used hydrogen-containing gas using a stripping column employing a hydrogen-containing gas as stripping gas; (iv) providing a second stream of hydrogen-containing gas which is heated within a section of a heating device which is arranged upstream of the first reactor to obtain a stream of heated hydrogen-containing gas; and (v) contacting in the second reactor at least part of the stream of heated hydrogen-containing gas as obtained in step (iv), optionally in the presence of at least part of the hydrotreated hydrocarbon oil as obtained in step (iii), with a second hydrotreating catalyst to obtain a stream of used hydrogen-containing gas, and a second effluent which comprises a further hydrotreated hydrocarbon oil when hydrotreated hydrocarbon oil as obtained in step (iii) is also present.
 2. A process according to claim 1, wherein the first stream of hydrogen-containing gas and the second stream of hydrogen-containing gas are derived from the same source of clean hydrogen-containing gas.
 3. A process according to claim 1, wherein the hydrocarbon oil to be hydrotreated is a gas oil which contains at least 75% by weight of hydrocarbons boiling in the range of from 150 to 400° C.
 4. A process according to claim 1, in which the hydrotreating conditions in steps (ii) and (v) comprise a temperature ranging from 250 to 480° C., a pressure from 10 to 150 bar, and a weight hourly space velocity of from 0.1 to 10 hr⁻¹.
 5. A process according to claim 1, wherein the second stream of hydrogen-containing gas contains less than 0.1% by volume of hydrogen sulphide.
 6. A process according to claim 1, wherein the first effluent as obtained in step (ii) is passed to a gas-liquid separator before using the stripping column.
 7. A process according to claim 1, wherein the used hydrogen-containing gas as obtained in step (iii) is cleaned and used again in step (v), and optionally in step (ii).
 8. A process according to claim 1, wherein step (v) is carried out in the presence of at least part of the hydrotreated hydrocarbon oil as obtained in step (iii).
 9. A process according to claim 1, wherein the hydrogen-containing gas that is being used as stripping gas in step (iii) has a temperature of from 250 to 480° C.
 10. A process according to claim 1, wherein the used hydrogen-containing gas as obtained in step (v) is used as stripping gas in step (iii).
 11. A process according to claim 1, wherein the first hydrotreating catalyst in step (ii) is a hydrodesulphurization catalyst and the second hydrotreating catalyst in step (v) is a hydrodewaxing catalyst.
 12. A process according to claim 11, wherein the hydrodesulphurization catalyst as used in step (ii) comprises one or more metals from Group VB, VIB and VIII of the Periodic Table of the Elements, on a solid carrier.
 13. A process according to claim 11, wherein the hydrodewaxing catalyst as used in step (v) comprises as catalytically active metal one or more noble metals from Group VIII of the Periodic Table of the Elements on a solid carrier. 